A quasi-periodic modulation of the iron line centroid energy in the black hole binary H1743−322

Abstract

Accreting stellar-mass black holes often show a `Type-C' quasi-periodic\noscillation (QPO) in their X-ray flux, and an iron emission line in their X-ray\nspectrum. The iron line is generated through continuum photons reflecting off\nthe accretion disk, and its shape is distorted by relativistic motion of the\norbiting plasma and the gravitational pull of the black hole. The physical\norigin of the QPO has long been debated, but is often attributed to\nLense-Thirring precession, a General Relativistic effect causing the inner flow\nto precess as the spinning black hole twists up the surrounding space-time.\nThis predicts a characteristic rocking of the iron line between red and blue\nshift as the receding and approaching sides of the disk are respectively\nilluminated. Here we report on XMM-Newton and NuSTAR observations of the black\nhole binary H 1743-322 in which the line energy varies systematically over the\n~4 s QPO cycle (3.70 sigma significance), as predicted. This provides strong\nevidence that the QPO is produced by Lense-Thirring precession, constituting\nthe first detection of this effect in the strong gravitation regime. There are\nhowever elements of our results harder to explain, with one section of data\nbehaving differently to all the others. Our result enables the future\napplication of tomographic techniques to map the inner regions of black hole\naccretion disks.\n